mirror of
https://github.com/google/pebble.git
synced 2025-03-15 08:41:21 +00:00
79 lines
2.7 KiB
Python
79 lines
2.7 KiB
Python
# Copyright 2024 Google LLC
|
|
#
|
|
# Licensed under the Apache License, Version 2.0 (the "License");
|
|
# you may not use this file except in compliance with the License.
|
|
# You may obtain a copy of the License at
|
|
#
|
|
# http://www.apache.org/licenses/LICENSE-2.0
|
|
#
|
|
# Unless required by applicable law or agreed to in writing, software
|
|
# distributed under the License is distributed on an "AS IS" BASIS,
|
|
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
# See the License for the specific language governing permissions and
|
|
# limitations under the License.
|
|
|
|
try:
|
|
import Queue
|
|
except ImportError:
|
|
# Py3 support
|
|
import queue as Queue
|
|
|
|
HDLC_FRAME_START = 0x7e
|
|
HDLC_ESCAPE = 0x7d
|
|
HDLC_ESCAPE_MASK = 0x20
|
|
|
|
|
|
class HDLCDecoder(object):
|
|
_STATE_SYNC, _STATE_DATA, _STATE_ESCAPE = range(3)
|
|
|
|
def __init__(self):
|
|
self._frames = Queue.Queue()
|
|
self._state = self._STATE_SYNC
|
|
self._buffer = bytearray()
|
|
|
|
def write(self, data):
|
|
for b in bytearray(data):
|
|
if self._state == self._STATE_SYNC:
|
|
# waiting for the first FRAME_START byte
|
|
if b == HDLC_FRAME_START:
|
|
self._state = self._STATE_DATA
|
|
elif self._state == self._STATE_DATA:
|
|
if b == HDLC_FRAME_START:
|
|
# this is the end of the frame (and the start of the next one)
|
|
if self._buffer:
|
|
self._frames.put_nowait(bytes(self._buffer))
|
|
self._buffer = bytearray()
|
|
elif b == HDLC_ESCAPE:
|
|
# escape the next byte
|
|
self._state = self._STATE_ESCAPE
|
|
else:
|
|
# this a valid byte of data
|
|
self._buffer.append(b)
|
|
elif self._state == self._STATE_ESCAPE:
|
|
if b == HDLC_FRAME_START:
|
|
# invalid byte combination - drop this frame and start the next one
|
|
self._buffer = bytearray()
|
|
else:
|
|
# escape this character
|
|
self._buffer.append(b ^ HDLC_ESCAPE_MASK)
|
|
self._state = self._STATE_DATA
|
|
else:
|
|
assert False, 'Invalid state!'
|
|
|
|
def get_frame(self):
|
|
try:
|
|
return self._frames.get_nowait()
|
|
except Queue.Empty:
|
|
return None
|
|
|
|
|
|
def hdlc_encode_data(data):
|
|
frame = bytearray()
|
|
frame.append(HDLC_FRAME_START)
|
|
for b in bytearray(data):
|
|
if b == HDLC_FRAME_START or b == HDLC_ESCAPE:
|
|
b ^= HDLC_ESCAPE_MASK
|
|
frame.append(HDLC_ESCAPE)
|
|
frame.append(b)
|
|
frame.append(HDLC_FRAME_START)
|
|
return bytes(frame)
|